The present invention relates to emulsions of fluorosilicone fluids in mineral oil, and to the use of these emulsions to suppress foam in organic liquids.
Silicones have long been recognized as foam suppressants. Methyl-substituted silicones are used extensively to suppress foam in aqueous media. Unfortunately, the methyl-substituted silicones are completely soluble in many organic liquids and therefore do not suppress foam in these liquids. In fact, methyl-substituted silicones sometimes even promote foam formation in organic liquids.
Currie, in U.S. Pat. No. 3,115,472, issued Dec. 24, 1963, disclosed, as an antifoam for organic solvents, solutions of perfluoroalkyl-substituted silicones in perchloroethylene or methyl-ethyl ketone. The presence of perfluoroalkyl substituents apparently changed the solubility characteristics sufficiently that foam suppression could be achieved in some organic liquids.
Michalski, in U.S. Pat. No. 3,660,305, issued May 2, 1972, disclosed a method of dispersing silicones such as perfluoroalkyl-substituted silicones. Michalski dispersed the silicone in an acetylenic alcohol.
Unfortunately, dispersions of perfluoro- alkyl-substituted silicones in polar solvents, such as methyl ethyl ketone, perchloroethylene and acetylenic alcohols, lose their efficacy as foam suppressants with time. This loss of efficacy is thought to be caused by depolymerization catalyzed by traces of acidic substances, said depolymerization being promoted by polar solvents.
Evans, in U.S. Pat. No. 4,329,528, issued May 11, 1982, disclosed a copolymer consisting of some dialkyl-substituted siloxy groups and some fluorinated alkyl-substituted siloxy groups. This copolymer apparently has the advantage of being at least partially soluble in some non-polar hydrocarbons. The copolymers, therefore, are more readily dispersible in organic liquids.
While each of the above references deals with the problem of dispersing fluorosilicone fluids so that they can be readily used to suppress foam in organic liquids, there is still a need to provide a simple and effective way of dispersing fluorosilicone fluids.
The present invention deals with novel emulsions of fluorosilicone fluids in mineral oil. The emulsion is stabilized by a particular polydimethylsiloxane-polybutadiene or polydimethylsiloxane-hydrogenated polybutadiene copolymer.
The term foam suppressant is to be understood in this specification to encompass the terms antifoaming agent and defoaming agent. Antifoaming is the prevention of foam in whole or in part. Defoaming is diminishing or eliminating an already existing foam.